1. Field of the Invention
The invention relates to a process for the preparation of a binder, the binder obtainable therefrom, the use thereof and the cured moldings produced therewith.
2. Discussion of Background Information
Sol-gel processes are based as a rule on the hydrolysis and condensation of alkoxides, as a rule in combination with silanes. These processes have long been known. Details of the sol-gel process are described, for example, in C. J. Brinker, G. W. Scherer: “Sol-Gel Science—The Physics and Chemistry of Sol-Gel-Processing”, Academic Press, Boston, San Diego, New York, Sydney (1990). A large number of compositions have been investigated. Orthosilicic esters have been used, for example, for more than 50 years as binders for refractory products. As long ago as 1939, Schröder and Geffcken filed patents for the coating of glasses by means of sol-gel processes. In the course of the decades, many industrial applications of sol-gel processes have become known, which as a rule concentrate on applications in the form of thin layers. Substantially based on the pioneering work of Schmidt et al., so-called hybrid materials in which organoalkoxysilanes were condensed together with alkoxides of other elements were developed, which gave so-called inorganic-organic hybrid materials, such as, for example, ormosils, ormocers, ceramers or polycerams.
Typical of these compounds is that they use the above-mentioned organoalkoxysilanes as a linking member to the organic moiety since silicon is virtually the only inorganic element which has a silicon-carbon bond stable under ambient conditions. By functionalizing the bond, any desired organic functions can be linked to the silicon. Owing to the hydrolyzable radicals of the alkoxysilane, inorganic networks can be built up by hydrolysis and condensation. Via the variations of the organic radical, virtually all functions which are known from organic chemistry can be introduced into the condensates.
Countless publications about this type of hybrid materials exist in the literature. Ormocers have also already become industrially important in large amounts for coating materials, for example as hard layers and corrosion protection layers. The silicon-oxygen-silicon bond constitutes an intrinsic disadvantage of these materials. Owing to its nature, it is sensitive to bases. Consequently, virtually no alkali-resistant coatings can be prepared using such systems. As our own investigations have shown, such systems are also sensitive to water at elevated pressure and elevated temperature, very particularly under hydrothermal conditions.
As is sufficiently known from the literature, a second network in the form of a polymeric chain can be incorporated by the use of polymerizable functional groups on the silicon if the polymerizable organic groups are linked to one another. In addition, it is also possible to add thereto organic monomers which then lead to longer organic polymeric chains. Such hybrid materials are designated as so-called IPN polymers (interpenetrating polymeric networks), cf. for example, Römpp Chemie Lexikon, 9th edition, page 2007. The interpenetrating networks may or may not be covalently linked to one another. In the latter case, a physical mixture is present. Different curing mechanisms may exist in such materials: firstly, the inorganic condensation in which silicon-oxygen-silicon bonds are established and, secondly, the organic linkage in which organic polymer chains form. If polyfunctional monomers are used, it is also possible to build up three-dimensional organic networks.
The organic polymer chains make it possible to change the mechanical properties of the materials. While the pure inorganic bonds lead to brittle materials which require temperatures above the transformation point (in the case of glasses) or above the crystallization temperature (in the case of ceramic materials) for compaction, hybrid materials can as a rule be compacted even at very low temperatures between 60 and 150° C.
While the inorganic materials are very stable to organic solvents or oils, materials which are based on organic polymer chains tend to swell or complete dissolution may occur, particularly at relatively high temperatures. Conversely, there are many organic polymers which are very alkali-stable. This means that an improvement in the alkali stability can be achieved by incorporating such polymers into the silicate networks. However, the fundamental dissolution of the silicate network by alkali attack or hydrothermal attack cannot be avoided. The silicon-oxygen-silicon bond is moreover reversible. While it can be formed by condensation from SiOH groups with elimination of water, it can undergo a reaction relatively rapidly back to SiOH groups with cleavage of the bond, particularly at high water vapour partial pressures and high temperatures.
In the case of the properties described above, such hybrid materials tend to undergo rapid decomposition under the hydrothermal conditions, particularly when organic solvents are also present. Thus, for example, our own investigations in autoclaves under simulated conditions which correspond, for example, to those at a water depth of 1000 m on binders having in principle a similar composition, as were proposed in U.S. Pat. No. 6,513,592 by PDVSA for fixing sand-containing deposits in mineral oil-containing formations, have shown that sand-containing moldings which have been bound with such binders to give compact bodies very rapidly undergo complete dissolution under these conditions in the autoclave. The dissolution process takes place particularly rapidly if a mixture of mineral oil and salt-containing water is used. This can be interpreted to mean that the hot water and the high pressure destroy the silicate bond and the crude mineral oil, which contains very many different compounds, including aggressive ones, attacks or dissolves the organic groups. Such binders are not suitable for the consolidation of loose formations, sands or rocks, as is of the greatest importance in mineral oil production.
The binders mentioned in DE-A-19647368 and DE-A-102004004615 for this application show improved stability but in principle also decompose under autoclave conditions of, for example, 70° C. at 70 bar.
Patent Application DE 102005002806.3 describes a process for the preparation of consolidated proppants in which a hydrolysis product or condensate of an organosilane, a hydrolyzable silane and a metal compound is used as a consolidating agent. These show substantially improved hydrolysis stability and corrosion stability under hydrothermal conditions, but a further improvement in the stability under said hydrothermal conditions is desirable and is a requirement in various cases for an application according to DE 102005002806.3.
It is known in the literature that glasses increase in hydrolysis stability by the incorporation of elements of the third and fourth main groups. Such elements are, for example, aluminum, zirconium or titanium. Boron, too, has such an effect, as do some divalent or trivalent elements, such as, for example, iron, calcium or lead. It is known that titanium has a particularly good effect if titanium is incorporated as a so-called network former in the glass structure.
The attempt to incorporate titanium via customary hydrolysis and condensation homogeneously or in molecular dispersion into hybrid structures cannot however be realized in practice owing to the very different reaction rates of titanium alkoxides and organoalkoxysilanes. On addition of water, nanoparticulate, in some cases already crystalline, particles form, which may be distributed in the matrix (also uniformly) but are not integrated in molecular or oligomeric form into the network. Consequently, the effect of alkali stability is not achieved because the portion of Si—O—Ti groups remains low. Accordingly, such hybrid materials, at least some of which are nanocomposites, were also substantially degraded in the autoclave test and show only little activity for the stable binding of sand-containing formations under such conditions.
The object was to provide binders which are absolutely stable under the above mentioned conditions and exhibit no degradation phenomena.